Method for locating impedance discontinuities in a wave propagating medium

ABSTRACT

A method for digitally processing seismic data, or other similar data derived for propagating wave energy to produce a data image comprised of a plurality of coordinate points is described. Each coordinate point has a value which is a combination of the amplitude values taken from a plurality of primary seismic traces at the travel times on the respective primary traces required for energy to travel from the respective source points to the coordinate point and return to the respective receiving points of the seismic traces. More particularly, the combination is accomplished in such a way as to increase the signal-to-noise ratio by selected data to be combined at the respective coordinate points either on a predetermined basis or automatically by an analysis of the data.

ilnited States atent Pizante METHOD FOR LOCATING IMPEDANCEDISCONTINUITIES IN A WAVE PROPAGATING MEDIUM Inventor: Jack H. Pizante,Richardson, Tex.

Texas Instruments Dallas, Tex.

July 8, 1970 Assignee: Incorporated, 4

Filed:

Appl. No.:

US. Cl...340/15.5 DP, 340/155 MC, 15.5 CC

Int. Cl. ..G0lv l/28 Field of Search ..340/l5.5 MC, 15.5 CC

[56] References Cited UNITED STATES PATENTS 51 Sept. 12, 1972 MelvinSharp and Richards, Harris and Hubbard [57] ABSTRACT A method fordigitally processing seismic data, or other similar data derived forpropagating wave energy to produce a data image comprised of a pluralityof coordinate points IS described. Each coordinate point has a valuewhich is a combination of the amplitude values taken from a plurality ofprimary seismic traces at the travel times on the respective primarytraces required for energy to travel from the respective source pointsto the coordinate point and return to the respective receiving points ofthe seismic traces. More particularly, the combination is accomplishedin such a way as to increase the signal-to-noise ratio by selected datato be combined at the respective coordinate points either on apredetermined basis or automatically by an analysis of the data.

19 Claims, 29 Drawing Figures TRACES AT STAT ION PATENTED SEP 12 m2SHEET 010F16 PATENTED s r 12 I972 SHEET OBUF 16l1u||||||||||||ll||||||||| y m I I I I I I I I I 1 I T 9 v l I I I l I ll I I I l I l 7 9 l I T- a 8 I I l l I I i I l I I l II n 9 l 0 On 9 I II I l I l I l I I i I l 0 I I l Il..|| V- 0 2 T a R SI 5 l I I I 3 R dNw T- a 2 I I l I i I l I I l l l I l l I l I I I II FIG. 4

lllll ll llllllll lllll e llllllllllllllllbnllllllllllbs 5. R b -s R bPATENTEDSEP 12 m2 SHEET OMUF 16 5 R b -S R b STATIONS FIG. 7

PATENTEDSEP l2 I972 SHEET 05 0F 16 IOI INVENTORI JACK H. P/ZANTE FIG. 8

PATENTEI] SEP 12 m2 SHEET 070! 16 STATIONS FIG. /2

INVENTORZ JACK H. PIZANTE PATENTEDSEP I 2 I972 INPUT TRACE P 4 SPREADTRACE (FIG. 4)

CORRECT FOR MOVEOUT (FIG.5)

SIIEEI UBIJF 16 INPUT TRACE IOOb SPREAD TRACE (FIG. 4)

INPUTPGI'RACE 3 SPREAD TRACE (FIG. 4)

l I I080 P b -Fa b CORRECT FOR MOVEOUT (FIG.5)

I I08b 5 o' s n TI CORRECT FOR MOVEOUT (FIGS) IOBc P b -P b I COLLATETRACES AT STATIONS T TRACES FOR STATION 94 (FIG.I2)

ISECTOR SELECTION I "1" CALCULATE CORRELATION GAIN J I I I COMBINETRACES I "1 COORDINATE VALUES FOR STATION 94 OF DATA IMAGE TRACES FORSTATION 95 (FIG.I2)

I l SECTOR sELECTION| "1 CALCULATE CORRELATION GAIN COMBINE TRACES I LCOORDINATE VALUES FOR STATION 95 OF DATA IMAGE FIG. I!

I TRACES FOR STATION 9 (FIG. I2)

I ISECTOR SELECTION "1 CALCULATE CORRELATION GAIN I I COMBINE TRACES I'9 COORDINATEVALUES FOR STATION 96 OF DATA IMAGE INVENTOR:

JACK H. P/ZANTE PATENTEUSEP I 2 I972 SHEET lUUF 16 lOl l 99 lC )O FIG./4

- INVENTOR:

JACK H. P/ZANTE FIG. I5

PATENTEDSEP 12 I972 SHEET 11 0F 16 FIG. /6

INVENTOR:

JACK H. P/ZANTE TRACES AT STATION PATENTED SEP 12 I972 SHEET 130F16INVENTOR:

JACK H. PIZANTE PAIENTEUSEP 12 m2 sum 1n 0F 16 IX WWW-M m WM III 228D229 b 230 b FIG. 25

ANGLE TRACES I-IX COMPUTE POWER CON T E NT AND SCALERS APPLY SCALERS TOTRACES I-IX STACK TRACES TO PRODUCE COORDINATE POINT VALUES AT STATION95 FIG.

INVENTOF:

JACK H. P/ZAN TE METHOD FOR LOCATING IMPEDANCE DISCONTINUITIES IN A WAVEPROPAGATING MEDIUM This invention relates generally to methods andapparatus for processing data representative of wave energy induced at asource point in a wave propagating medium and detected at a receivingpoint in such a manner as to produce a data image of discontinuitieswithin the medium. The invention is specifically related to methods fordetermining the location of both diffraction and reflection typeacoustic impedance discontinuities of a planet such as Earth.

Extensive research efforts have been expended in recent decades toperfect the art of Seismology. Recent events indicate that one of themore significant developments in this art is the method for processingseismic data described and claimed in, US. Pat. No. 3,353,151, entitledCommon Tangent Stacking Method And System For Locating Sonic EnergyVelocity Discontinuities, issued to D. W. Rockwell on Nov. 14, 1967, andassigned to the assignee of this invention.

The Rockwell patent discloses a method for processing seismic datawherein each seismic response record, commonly referred to as a trace,is plotted by either analog or digital apparatus, as a scaled wavefrontpattern. Each coordinate point of the scaled wavefront pattern has theamplitude value at the travel time on the trace required for the energyto travel from the source point to the coordinate position and then backto the receiving point. The amplitude values of the scaled wavefrontpatterns derived from a plurality of traces are then combined atcorresponding coordinate points which results in a composite image ofthe acoustic impedance discontinuities of the subsurface. Stated anotherway, imagine the volume being explored as a three-dimensional grid. Foreach source-receiver trace recorded, the travel time from the source toa grid point in the volume and back to the receiver is calculated. Theamplitude value of the recorded trace, observed at the calculated time,is added to an accumulating sum associated with the grid point. Theresulting set of values obtained over a region of the subsurface grid,as a result of accumulating data from many sourcereceiver traces, willthen show large values at the location of subsurface scatters, such asfault planes, dome boundaries, reefs, unconformities, pinchouts,cavities, rough boundaries, etc., as well as reflecting interfaces. Thegrid of numbers may be displayed in a number of conventional ways. Thecomposite image so produced has recently been recognized as a form ofacoustic hologram, and the method a form of acoustic holography.

There are many advantages of the Rockwell method when compared toprevious data processing methods. Perhaps the most significant advantageis that each incremental time interval is plotted in the true migratedmode with respect to either two or three-dimensional space. The methodtends to automatically enhance the signal-to-noise ratio. No specialconstraints in the geometry of the source and receiver are required. Theprocess is applicable to either reflection, diffraction or refractionenergy, and in particular provides, for the first time, a practicalmethod for locating energy diffractors or scatterers.

The present invention is concerned with an improvement in the methoddescribed and claimed in the above referenced Rockwell patent, and moreparticularly relates to a method for processing the data so as tofurther enhance the signal-to-noise ratio and to thus better identifyand locate both reflectors and diffractors.

In accordance with this invention, each input trace, derived either froma single source-receiver pair or by stacking the traces from a pluralityof source-receiver pairs, is spread to a number of horizontally spacedstations. Then each spread trace is corrected for moveout to therespective station based on the locations of the source and receiver forthe input trace relative to the station so that each of the spreadtraces is corrected to verticality. Then the vertically corrected tracesat each interval are combined in a predetermined manner to produce acomposite data image. The data image is a coordinate grid. The value ateach coordinate point of the grid is a positive or negative value, andthe image may be further processed for display in any conventionalmanner.

More specifically, the invention contemplates enhancement of thecomposite data image by controlling, either on a predetermined or anautomatic basis, the input traces which are to contribute data tocertain areas of the composite image. In accordance with a specificaspect of the invention, the detection of specular reflectors isenhanced by selecting only a portion of the vertically corrected tracesat the respective stations for combination to produce the composite dataimage based on a predetermined range of dip angles for the reflectors.This selection may include a scaling or weighting of the values, and maychange with depth.

In accordance with another aspect of the invention, specular reflectorscan be enhanced by automatically increasing the amplitude values ofcertain of the vertically corrected traces in accordance with the degreeof correspondence between the amplitude values of a particular trace andthe amplitude values of one or more collateral traces at the traveltimes on the collateral traces where energy reflected from the saiddiscontinuity would be found if a discontinuity existed.

In accordance with still another aspect of the invention, the image ofscattering or diffracting discontinuities can be enhanced byautomatically increasing the amplitude values of the verticallycorrected traces at each station in accordance with the degree ofcorrespondence between said amplitude values and the amplitude values onone or more collateral traces at the travel times where energy would bereturned from a diffracting discontinuity located at the pointrepresented by said amplitude values.

The novel features believed characteristic of this invention are setforth in the appended claims. The invention itself, however, as well asother objects and advantages thereof, may best be understood byreference to the following detailed description of illustrativeembodiments, when read in conjunction with the accompanying drawings,wherein:

FIG. 1 is a schematic representation of a two-dimensional composite dataimage in accordance with the present invention;

FIG. 2 is a schematic diagram illustrating a conventional method ofcollecting multicoverage seismic data using common depth point geometrywhich can also be advantageously processed by the method of the presentinvention;

FIG. 3 is a block diagram which illustrates one embodiment of the methodof the present invention;

FIG. 4 is a schematic diagram which illustrates one step of the methodrepresented in FIG. 3;

FIG. 5 is a schematic diagram which illustrates another step in themethod represented in FIG. 3;

FIG. 6 is a schematic diagram which also illustrates the method stepillustrated in FIG. 5;

FIG. 7 is a table setting forth the traces which are assigned to therespective stations in accordance with the method of FIG. 3;

FIG. 8 is a schematic diagram which serves to illustrate the criteriafor the step of sector selecting in the method of FIG. 3;

FIG. 9 is a schematic diagram illustrating the method of automaticsector selection by correlation gain in the method of FIG. 3;

FIG. 9a is a schematic diagram illustrating a method for determiningcorrelation gain in the sector selecting step of FIG. 9;

FIG. 10 is a schematic diagram illustrating sector selection byautomatic correlation gain for diffractors in the method of FIG. 3;

FIG. 11 is a block diagram of another embodiment of the method of thepresent invention;

FIG. 12 is a table illustrating the manner in which traces are collatedat the respective stations in the method of FIG. 11;

FIG. 13 is a schematic diagram which illustrates specific aspects of themethod of FIG. 11;

FIGS. 14-17 are schematic diagrams which illustrate how the datadisplayed in FIG. 13 is interpreted;

FIGS. 18-21 are schematic diagrams illustrating amplitude profiles ofthe data displayed in FIG. 13 at depths Z,,-Z,,, respectively;

FIG. 22 is a schematic diagram which illustrates advantages of themethod of the present invention;

FIG. 23 is a schematic diagram which illustrates another embodiment ofthe method of the present invention for automatic sector control;

FIG. 24 is a block diagram of the embodiment of the inventionillustrated in FIG. 23;

FIG. 25 is a schematic diagram which illustrates one aspect of theembodiment of FIG. 23;

FIG. 26 is a schematic drawing which illustrates application of themethod of the present invention to produce a three-dimensional dataimage;

FIG. 27 is another schematic drawing which illustrates the applicationof the present invention to produce a three-dimensional image from aplurality of sets of common depth point data; and

FIG. 28 is a schematic diagram which illustrates one step of the methodas applied to the production of a three-dimensional data image.

Referring now to the drawings, FIG. 1 illustrates schematically the typeof data image which is to be produced in accordance with the presentinvention. A datum line D represents a horizontal line which mayapproximate the surface-air interface of the Earth. The datum line D isdivided at equal horizontal intervals to provide stations 86-100, which,of course, may be only one portion of the total image. The data image iscomprised of a plurality of coordinate points 10 arranged at equalvertical intervals under each of the stations 86-100 on the datum lineD. The stations on the datum line D are typically to feet apart, whilethe vertical intervals between the coordinate points 10 may be expressedeither in equal time increments, or equal depth increments. In eithercase, the increments will typically represent from 25 to 50 feet. Thevertical intervals will hereafter be expressed in depth for convenienceunless otherwise stated, although it will be understood that the methodmay be practiced using either the time or depth domain as in moreconventional common depth point stacking.

Each of the coordinate points 10 is comprised of a numerical value,either positive or negative, which is usually expressed in digitalmachine language. The value at each of the coordinate points of the dataimage is derived by combining a plurality of amplitude values taken froma plurality of input traces derived from source-receiver pairs as willhereafter be described in detail. The data image shown in FIG. I is thetype described in the above referenced Rockwell patent. This inventionis concerned with an improved method for processing the data to producea data image having enhanced images.

A conventional method for collecting seismic data, commonly referred toas the common depth point method is illustrated in FIG. 2. In FIG. 2,lines 10a-10c represent the surface of either land or water, whichoverlies a subsurface region in which it is desired to map the acousticimpedance discontinuities.

Assume that seismic energy is first induced at a source point 5,,commonly referred to as a shot point, using any conventional means, suchas an explosive charge, gas exploder, hydraulic thumper, weight drop orthe like. Assume also that shot point S is horizontally located atstation 90 on datum line D, although the shot point S, may be above orbelow the elevation of the datum line. An array of receivers is disposedon the surface 10a to one side of shot point S, with the receiverslocated at stations 92, 94, 96, etc. 24 receivers are typically usedalthough only receivers R,-R are illustrated in FIG. 2. It should benoted that the receivers are uniformly spaced, and that shot point S, istypically spaced from receiver R, by a distance equal to the spacingbetween the receivers. The acoustic return detected at receivers R,-Rtogether with that detected at the other 19 receivers of the spread istypically recorded on a single 24 trace seismogram. These traces may beindividually identified by a combination of the shot point designationand the receiver designation, such as traces S,R,-S,R respectively. Thevalues of each of the traces of the seismogram are preferably digitalvalues representing both the amplitude and the phase of the detectedacoustic energy. The digital values are typically produced by samplingthe detected analog signal at time intervals of one, 2 or 4 millisecondsand are recorded on a single multiplexed channel.

After the first seismogram is produced from energy induced at shot point5,, the source is indexed to station 88, as represented by shot point Sand each of the receivers R,-R is also indexed two stations, asillustrated on line 10b, and the shooting process repeated. Thisproduces a second seismogram containing 24 traces, which traces can beidentified as traces 8 R,- S R respectively. The shooting procedure isthen repeated with shot point 5;, at station 86 and the receivers Il -Rspread at the stations illustrated on line 100. The shooting procedureis repeated every two stations with the appropriate movement of thereceiver spread until the entire area of interest is completed. It isimportant to understand that the relationship between the shot points,receivers and stations is not critical to the invention, but is aconvenience for handling the data in an orderly fashion. In general, awider spread of stations contributing to the image provides a greaterhorizontal resolution, and a closer density of stations provides greatervertical resolution in the composite data image.

Seismic data collected in this manner is referenced to as common depthpoint data. Common depth point data is chosen to illustrate the methodof the present invention because the method is ideally suited to processsuch data, and vast quantities of common depth point data heretoforecollected can be advantageously processed in accordance with the methodof the present invention to yield better information about thesubsurface region than was heretofore possible. However, it is importantto understand that the method of the present invention is not limited tocommon depth point data, but is applicable in its broader aspects todata representative of any wave energy induced at a source point anddetected at a receiving point on or within a wave propagating mediumsuch as the Earth, the human body, or any other solid liquid or gaseousbody, or even outer space when using energy, such as electromagneticwave energy, which will propagate through space.

Although the highly ordered nature of common depth point data simplifiesdata processing, it is to be understood that this invention requires noconstraints upon the relative positions of the shot points and thereceivers. The receivers need not be spaced at equal horizontalintervals, nor do the successive shot points need be spaced at equalhorizontal intervals. Further neither the shot points nor the receiversneed to be arrayed in a straight line, as is required for common depthpoint data. The shot points and the receivers may thus be located at anyposition, so long as the location of these positions are known. Further,a two-dimensional spread of shot points and receivers can be used toachieve a three-dimensional data image from which any desiredtwo-dimensional section, vertical, horizontal, or at any angle, can beextracted for display, or which may be displayed using three-dimensionaldisplay techniques as stereo pairs, holograms, or more conventionalthree-dimensional drawings.

Each of the 24 traces S R S R on each of the seismograms produced fromshots S S,,, respectively, may be an input trace for the methodillustrated in FIG. 3, and in all specific examples hereafter discussed,it is assumed that such is the case. However, it is to be understoodthat the input traces may be preprocessed in substantially anyconventional manner prior to input to the method illustrated in FIG. 3,such as for example, to move the shot points and receivers to the datumline, correct for the overburden, or similar techniques. For bestresults, however, it is desirable to use original traces prior to commondepth point stacking since such stacking distorts the data. However,because of the very large number of traces typically produced whencollecting common depth point data, it may be desirable to select only aportion of the total numbered traces derived from differentsource-receiver pairs for processing in order to reduce the operatingtime of the digital computer. For some applications, common depth pointstacked traces may be used as the input traces to the method, ashereafter described in connection with the embodiment of FIG. 11.

FIG. 3 is a block diagram illustrating the manner in which input tracesS R 8 R, and S,R,, for example, would be processed by a digital computerin ac cordance with one embodiment of the present invention. In general,all input traces are processed in parallel as indicated by the identicalvertical flow paths for the input traces S R S,R and SR, shown in FIG.3. For example, the input traces S R- S,R and S R are first spread asrepresented at blocks 20a, 20b and 20c, respectively.

The spreading operation of block 20a, for example, is illustrated indetail in FIG. 4 and comprises merely reproducing the input trace S R toproduce a plurality of identical traces S,R a S,R- a,,. Since shot pointS was located at station and receiver R at station 94, the traces S R aS,R a,, are spread consecutively from station 92, which is the centerpoint between shot point 8, and receiver R over the higher numberedstations. It will be noted that this occupies only a half space of thetotal sector from which the acoustic energy could have been returned tothe receiver. Assuming that the acoustic velocity is the same on eachside of the center point of the spread, traces S,R a S,R a,,, and allfurther traces derived therefrom, can be reproduced beginning at station92 and proceeding to lower numbered stations. If the velocity is not thesame when propagating in different directions from the center point, theprocessing of traces S,R a,S R a,, can be repeated using differentvelocity values and the traces designated by different characters, suchas by -S,R a through -S,R a,,. Since the traces S R a -S,R a,, aremerely duplications of the input trace S R the amplitude values attravel time T,- on all traces would appear at the same apparent depth asillustrated in FIG. 4.

The outputs from steps 20a-20c are spreads of traces S1 2l o i 2 n, 1R3o 1R3 n n I 4 O I 4 n, which are represented by blocks 21a-21c,respectively, in FIG. 3, and which are assigned to the stations according to the table of FIG. 7.

Next, each of the spreads of traces 2la-2lc is corrected for moveout asrepresented by blocks 22a-22c, with spread 21a being illustrated indetail in FIGS. 5 and 6, to produce spreads 230-230, respectively, whichincludes traces S,R b S R b,,, S R b -S R b,,, and S R b S,R b,.,respectively. Each trace of each spread 2311-230 is comprised of aseries of amplitude values sampled at uniform depth intervals, and arethus equivalent to a series of vertically spaced coordinate points. Asmentioned previously, these uniform depth intervals can be uniformelapsed time intervals, rather than depth intervals. The depth intervalsof the trace spreads 23a-23c are conveniently the same depth in tervalsas the coordinate points 10 of the composite data image illustrated inFIG. 1, although for some purposes it may be desirable to retain greaterresolution by

1. The method for determining the location of impedance discontinuitiesin a wave propagating medium from a plurality of digital input traceseach representative of wave energy returning to a receiving point fromwave energy induced at a source point which comprises, in an automaticdata processing machine, computing a moveout trace from each input tracefor each of a predetermined number of stations, each moveout tracehaving amplitude values at coordinate depth points representative of theamplitude values at the travel time on the input trace required forenergy to travel from the source point of the input trace to therespective coordinate depth point of the respective station to thereceiving point for the input trace, partitioning the amplitude valuesof the moveout traces for each station into a plurality of subsets ofamplitude values, each subset comprising the amplitude values whichwould be located generally in pie-slice shaped sections defined by linesdiverging from the datum point of the station generally at an angle ifthe moveout traces were positioned at points corresponding to themidpoints between the source and receiver points for the input tracefrom which the respective moveout trace was derived, weighting theamplitude values at the respective depth points within each subset as afunction of the degree of correlation of the amplitude values in thesubset over a depth interval in which the respective depth points arelocated, and combining the weighted values of the moveout traces foreach station to produce composite values for the coordinate depth pointsat the respective stations to form a data image.
 2. The method of claim1 wherein the coordinate depth points for the moveout traces are ingenerally parallel columns lying generally within a plane.
 3. The methodof claim 1 wherein the stations are arrayed generally in a datum planeand the coordinate depth points for the moveout traces are in generallyparallel columns extending from the respective stations at an angle fromthe datum plane, and each subset includes amplitude values from pointswhich would be located generally in a three dimensional region definedby at least three lines not in a common plane and diverging generallyfrom the respective stations in the datum plane.
 4. The method fordetermining the location of impedance discontinuities in a wavepropagating medium from a plurality of digital input traces eachrepresentative of wave energy returning to a receiving point from waveenergy induced at a source point which comprises, in an automatic dataprocessing machine, computing a moveout trace from each input trace foreach of a predetermined number of stations, each moveout trace havingamplitude values at coordinate depth points representative of theamplitude values at the travel time on the input trace required forenergy to travel from the source point of the input trace to thecoordinate depth point of the station to the receiving point for theinput trace, partitioning the amplitude values of the moveout traces foreach station into a plurality of subsets of amplitude values, eachsubset including the portions of the amplitude values of the traces inpredetermined geometric locations relative to the source and receivingpoints for the input traces from which the respective amplitude valueswere derived, stacking the amplitude values at the same depth pointswithin each subset to produce a stacked trace for each subset ofamplitude values, weighting the values of each of the stacked traces atthe respective depth points as a function of the degree of correlationof the stacked trace over a depth interval in which the respective depthpoints are located, and combining the weighted values of the stackedtraces to produce composite values for the coordinate points to form adata image.
 5. The method of claim 4 wherein the values are weighted inaccordance with the relative power content of the stacked traces overcorresponding depth intervals.
 6. The method of claim 4 wherein theamplitude values of the moveout traces are partitioned such that thesubsets of amplitude values would be located in generally pie-shapedsegments if the moveout traces were positioned at the stationscorresponding to the midpoints between the source and receiver pointsfor the input trace from which the respective moveout traces werederived.
 7. The method of claim 4 wherein the amplitude values areweighted by summing the squares of the values of each stacked tracewithin each of a series of depth intervals to produce a power factor foreach of the stacked traces for the depth intervals, producing a scalerfor each stacked trace for each coordinate depth point based upon thepower factor for the depth interval in which the coordinate depth pointis located, applying the scalers to the values of the stacked traces toweight the values of the stacked traces, and then combining the weightedstacked amplitude values to produce composite values for the respectivecoordinate depth points.
 8. The method of claim 7 wherein the amplitudevalues of the moveout traces are partitioned such that the amplitudevalues of each subset would be located generally in segments bounded bylines diverging from the station if the moveout traces were located atthe midpoints between the source and the receiver points for the inputtrace from which the respective moveout traces were derived.
 9. Themethod of claim 7 whereIn the depth intervals over which the powerfactors are computed are contiguous, the scalers for the coordinatedepth points at the midpoints of the depth intervals are equal to thepower factor for the intervals of the respective stacked trace dividedby the sum of the power factors for the corresponding intervals for allof the stacked traces, and the scalers for the coordinate depth pointsbetween the midpoints of the depth intervals are linear interpolationsbetween the scalers for the depth points at the midpoints of theintervals.
 10. The method for determining the location of impedancediscontinuities in a wave propagating medium from a plurality of digitalinput traces each representative of wave energy returning to a receivingpoint from wave energy induced at a source point which comprises, in anautomatic data processing machine, defining a set of stations athorizontal intervals on a horizontal datum line representing generallythe surface of the earth and a set of coordinate depth points below eachstation, computing a plurality of moveout traces for each station havingan amplitude value for each coordinate point below the station, eachmoveout trace for each station being computed from a different inputtrace, each moveout trace having amplitude values at coordinate depthpoints representative of the amplitude values at the travel time on therespective input traces required for energy to travel from the sourcepoint of the respective input trace to the respective coordinate depthpoint to the receiving point for the respective input trace,partitioning the amplitude values of the moveout traces for each stationinto a plurality of subsets of amplitude values, each subset comprisingthe amplitude values which would be located generally in segmentsdefined by lines diverging from the station to create generallypie-shaped sections if the moveout traces were positioned at positionscorresponding to the midpoints between the source and receiver pointsfor the input traces from which the respective moveout traces werederived, stacking the amplitude values at corresponding depth pointswithin each subset of amplitude values to produce an angle trace foreach subset having a stacked amplitude value for each of the coordinatedepth points, computing a power factor for predetermined depth intervalsof each of the angle traces, computing a scaler for each stackedamplitude value of each of the angle traces that is a function of thepower factor for the depth interval in which the amplitude value islocated, applying each scaler to each amplitude value of each of theangle traces to produce a scaled value, and combining the scaled valuesto produce a composite value for each coordinate depth point and therebyform a data image.
 11. The method of claim 10 wherein the scaler foreach stacked amplitude value is the power factor for the respectivestacked amplitude value divided by a reference value, the stackedamplitude values of the angle traces are multiplied by the respectivescalers in succession and the scaled values combined in a partial sumuntil a total sum for the scaled values at the coordinate depth point ofall the angle traces is produced, and the total sum for each depth pointis multiplied by a recovery scaler which is the reference value dividedby the sum of the power factors for all of the angle traces at thecoordinate depth point.
 12. The method for determining the location ofimpedance discontinuities in a wave propagating medium from a pluralityof digital input traces each representative of wave energy returning toa receiving point from wave energy induced at a source point whichcomprises, in an automatic data processing machine, defining a set ofstations at generally uniform horizontal intervals on a horizontal datumline representing generally the surface of the earth, and a set ofcoordinate depth points below each station, computing a plurality ofmoveout traces for each station having an amplitude value for eachcoordinate point below the station, each moveout trace for each stationbeing computed from different input traces, each moveout trace havingamplitude values at coordinate depth points representative of theamplitude values at the travel time on the respective input tracesrequired for energy to travel from the source point of the respectiveinput trace to the respective coordinate depth point to the receivingpoint for the respective input trace, partitioning the amplitude valuesof the moveout traces for each station into a plurality of subsets ofamplitude values, each subset comprising amplitude values which would belocated in predetermined geometric sections if the moveout traces werepositioned at positions corresponding to the midpoints between thesource and receiver points for the input traces from which therespective moveout traces were derived, producing a correlation factorrepresentative of the degree of correspondence of the amplitude valueswithin a series of depth intervals of each subset, computing a scalerfor the amplitude values at each coordinate depth point of each of thesubsets that is a function of the correlation factor for the depthinterval of the subset of the amplitude value, applying each scaler tothe amplitude value to produce a scaled value, and combining the scaledvalues to produce a composite value for each coordinate depth point andthereby form a data image.
 13. The method of claim 12 wherein the scalerfor each stacked amplitude value is the power factor for the respectivestacked amplitude value divided by a reference value, the stackedamplitude values of the angle traces are multiplied by the respectivescalers in succession and the scaled values combined in a partial sumuntil a total sum for the scaled values at the coordinate depth point ofall the angle traces is produced, and the total sum for each depth pointis multiplied by a recovery scaler which is the reference value dividedby the sum of the power factors for all of the angle traces at thecoordinate depth point.
 14. The method for determining the location ofimpedance discontinuities in a wave propagating medium from a pluralityof digital input traces each representative of wave energy returning toa receiving point from wave energy induced at a source point whichcomprises, in an automatic data processing machine, defining a dataimage in at least two dimensions by a set of coordinate depth pointsarranged in columns under a plurality of stations, producing a set ofamplitude values for each coordinate point, each amplitude value of eachset being representative of the amplitude value at the time on adifferent input trace required for energy to travel from the sourcepoint of the respective input trace to the coordinate depth point to thereceiving point for the respective input trace, partitioning theamplitude values for the coordinate depth points under each station intoa plurality of subsets of amplitude values based on the geometriclocation of the respective amplitude values if positioned at thecorresponding depth under the midpoint between the source and receivingpoints for the respective input traces from which the amplitude valuewas derived, producing a correlation factor representative of the degreeof correspondence of the amplitude values within a series of depthintervals of each subset, computing a scaler for the amplitude values ateach coordinate depth point of each of the subsets that is a function ofthe correlation factor for the depth interval of the subset of theamplitude value, applying each scaler to the amplitude value to producea scaled value, and combining the scaled values to produce a compositevalue for each coordinate depth point.
 15. The method of claim 14wherein the scaler for each stacked amplitude value is the power factorfor the respective stacked amplitude value dividEd by a reference value,the stacked amplitude values of the angle traces are multiplied by therespective scalers in succession and the scaled values combined in apartial sum until a total sum for the scaled values at the coordinatedepth point of all the angle traces is produced, and the total sum foreach depth point is multiplied by a recovery scaler which is thereference value divided by the sum of the power factors for all of theangle traces at the coordinate depth point.
 16. The data image producedin an automatic data processing machine for determining the location ofimpedance discontinuities in a wave propagating medium from a pluralityof digital input traces each representative of wave energy returning toa receiving point from wave energy induced at a source point bycomputing a moveout trace from each input trace for each of apredetermined number of stations, each moveout trace having amplitudevalues at coordinate depth points representative of the amplitude valuesat the travel time on the input trace required for energy to travel fromthe source points of the input trace to the respective coordinate depthpoint of the respective station to the receiving point of the inputtrace, partitioning the amplitude values of the moveout traces for eachstation into a plurality of subsets of amplitude values, each subsetcomprising the amplitude values which would be located generally inpie-slice shaped sections defined by lines diverging from the datumpoint of the station generally at an angle if the moveout traces werepositioned at points corresponding to the midpoints between the sourceand receiving points for the input trace from which the respectivemoveout trace was derived, weighting the amplitude values at therespective depth points within each subset as a function of the degreeof correlation of the amplitude values in the subset over a depthinterval in which the respective depth points are located, and combiningthe weighted values of the moveout traces for each station to producecomposite values for the coordinate depth points at the respectivestations.
 17. The data image produced in an automatic data processingmachine to determine the location of impedance discontinuities in a wavepropagating medium from a plurality of digital input traces eachrepresentative of wave energy returning to a receiving point from waveenergy induced at a source point by computing a moveout trace from eachinput trace for each of a predetermined number of stations, each moveouttrace having amplitude values at coordinate depth points representativeof the amplitude values at the travel time on the input trace requiredfor energy to travel from the source point of the input trace to thecoordinate depth point of the station to the receiving point for theinput trace, partitioning the amplitude values of the moveout traces foreach station into a plurality of subsets of amplitude values, eachsubset including the portions of the amplitude values of the traces inpredetermined geometric locations relative to the source and receivingpoints for the input traces from which the respective amplitude valueswere derived, stacking the amplitude values at the same depth pointswithin each subset to produce a stacked trace for each subset ofamplitude values, weighting the values of each of the stacked traces atthe respective depth points as a function of the degree of correlationof the stacked trace over a depth interval in which the respective depthpoints are located, and combining the weighted values of the stackedtraces to produce composite values for the coordinate points.
 18. Thedata image produced in at automatic data processing machine to determinethe location of impedance discontinuities in a wave propagating mediumfrom a plurality of digital input traces each representative of waveenergy returning to a receiving point from wave energy induced at asource point by defining a set of stations at horizontal intervals on ahorizontal data line Representing generally the surface of the earth anda set of coordinate depth points below each station, computing aplurality of moveout traces for each station having an amplitude valuefor each coordinate point below the station, each moveout trace for eachstation being computed from a different input trace, each moveout tracehaving amplitude values at coordinate depth points representative of theamplitude values at the travel time on the respective input tracesrequired for energy to travel from the source point of the respectiveinput trace to the respective coordinate depth point to the receivingpoint for the respective input trace, partitioning the amplitude valuesof the moveout traces for each station into a plurality of subsets ofamplitude values, each subset comprising the amplitude values whichwould be located generally in segments defined by lines diverging fromthe station to create generally pie-shaped sections if the moveouttraces were positioned at positions corresponding to the midpointsbetween the source and receiver points for the input traces from whichthe respective moveout traces were derived, stacking the amplitudevalues at corresponding depth points within each subset of amplitudevalues to produce an angle trace for each subset having a stackedamplitude value for each of the coordinate depth points, computing apower factor for predetermined depth intervals of each of the angletraces, computing a scaler for each stacked amplitude value of each ofthe angle traces that is a function of the power factor for the depthinterval in which the amplitude value is located, applying each scalerto each amplitude value of each of the angle traces to produce a scaledvalue, and combining the scaled values to produce a composite value foreach coordinate depth point.
 19. The data image produced in an automaticdata processing machine to determine the location of impedancediscontinuities in a wave propagating medium from a plurality of digitalinput traces each representative of wave energy returning to a receivingpoint from wave energy induced at a source point by defining a set ofstations as generally uniform horizontal intervals on a horizontal datumline representing generally the surface of the earth, and a set ofcoordinate depth points below each station, computing a plurality ofmoveout traces for each station having an amplitude value for eachcoordinate point below the station, each moveout trace for each stationbeing computed from different input traces, each moveout trace havingamplitude values at coordinate depth points representative of theamplitude values at the travel time on the respective input tracesrequired for energy to travel from the source point of the respectiveinput trace to the respective coordinate depth point to the receivingpoint for the respective input trace, partitioning the amplitude valuesof the moveout traces for each station into a plurality of subsets ofamplitude values, each subset comprising amplitude values which would belocated in predetermined geometric sections if the moveout traces werepositioned at positions corresponding to the midpoints between thesource and receiver points for the input traces from which therespective moveout traces were derived, producing a correlation factorrepresentative of the degree of correspondence of the amplitude valueswithin a series of depth intervals of each subset, computing a scalerfor the amplitude values at each coordinate depth point of each of thesubsets that is a function of the correlation factor for the depthinterval of the subset of the amplitude value, applying each scaler tothe amplitude value to produce a scaled value, and combining the scaledvalues to produce a composite value for each coordinate depth point.